Platelet-derived growth factor receptor ß-targeted positron emission tomography imaging for the noninvasive monitoring of liver fibrosis.

PURPOSE: Noninvasive quantifying activated hepatic stellate cells (aHSCs) by molecular imaging is helpful for assessing disease progression and therapeutic responses of liver fibrosis. Our purpose is to develop platelet-derived growth factor receptor ß (PDGFRß)-targeted radioactive tracer for assessing liver fibrosis by positron emission tomography (PET) imaging of aHSCs. METHODS: Comparative transcriptomics, immunofluorescence staining and flow cytometry were used to evaluate PDGFRß as biomarker for human aHSCs and determine the correlation of PDGFRß with the severity of liver fibrosis. The high affinity affibody for PDGFRß (ZPDGFRß) was labeled with gallium-68 (68Ga) for PET imaging of mice with carbon tetrachloride (CCl4)-induced liver fibrosis. Binding of the [68Ga]Ga-labeled ZPDGFRß ([68Ga]Ga-DOTA-ZPDGFRß) for aHSCs in human liver tissues was measured by autoradiography. RESULTS: PDGFRß overexpressed in aHSCs was highly correlated with the severity of liver fibrosis in patients and CCl4-treated mice. The 68Ga-labeled ZPDGFRß affibody ([68Ga]Ga-DOTA-ZPDGFRß) showed PDGFRß-dependent binding to aHSCs. According to the PET imaging, hepatic uptake of [68Ga]Ga-DOTA-ZPDGFRß increased with the accumulation of aHSCs and collagens in the fibrotic livers of mice. In contrast, hepatic uptake of [68Ga]Ga-DOTA-ZPDGFRß decreased with spontaneous recovery or treatment of liver fibrosis, indicating that the progression and therapeutic responses of liver fibrosis in mice could be visualized by PDGFRß-targeted PET imaging. [68Ga]Ga-DOTA-ZPDGFRß also bound human aHSCs and visualized fibrosis in patient-derived liver tissues. CONCLUSIONS: PDGFRß is a reliable biomarker for both human and mouse aHSCs. PDGFRß-targeted PET imaging could be used for noninvasive monitoring of liver fibrosis in mice and has great potential for clinical translation.

Retinal inflammation in murine models of type 1 and type 2 diabetes with diabetic retinopathy.

AIMS/HYPOTHESIS: The loss of pericytes surrounding the retinal vasculature in early diabetic retinopathy underlies changes to the neurovascular unit that lead to more destructive forms of the disease. However, it is unclear which changes lead to loss of retinal pericytes. This study investigated the hypothesis that chronic increases in one or more inflammatory factors mitigate the signalling pathways needed for pericyte survival. METHODS: Loss of pericytes and levels of inflammatory markers at the mRNA and protein levels were investigated in two genetic models of diabetes, Ins2Akita/+ (a model of type 1 diabetes) and Leprdb/db (a model of type 2 diabetes), at early stages of diabetic retinopathy. In addition, changes that accompany gliosis and the retinal vasculature were determined. Finally, changes in retinal pericytes chronically incubated with vehicle or increasing amounts of IFNγ were investigated to determine the effects on pericyte survival. The numbers of pericytes, microglia, astrocytes and endothelial cells in retinal flatmounts were determined by immunofluorescence. Protein and mRNA levels of inflammatory factors were determined using multiplex ELISAs and quantitative reverse transcription PCR (qRT-PCR). The effects of IFNγ on the murine retinal pericyte survival-related platelet-derived growth factor receptor ß (PDGFRß) signalling pathway were investigated by western blot analysis. Finally, the levels of cell death-associated protein kinase C isoform delta (PKCδ) and cleaved caspase 3 (CC3) in pericytes were determined by western blot analysis and immunocytochemistry. RESULTS: The essential findings of this study were that both type 1 and 2 diabetes were accompanied by a similar progression of retinal pericyte loss, as well as gliosis. However, inflammatory factor expression was dissimilar in the two models of diabetes, with peak expression occurring at different ages for each model. Retinal vascular changes were more severe in the type 2 diabetes model. Chronic incubation of murine retinal pericytes with IFNγ decreased PDGFRß signalling and increased the levels of active PKCδ and CC3. CONCLUSIONS/INTERPRETATION: We conclude that retinal inflammation is involved in and sustains pericyte loss as diabetic retinopathy progresses. Moreover, IFNγ plays a critical role in reducing pericyte survival in the retina by reducing activation of the PDGFRß signalling pathway and increasing PKCδ levels and pericyte apoptosis.

Long Noncoding RNA TYKRIL Plays a Role in Pulmonary Hypertension via the p53-mediated Regulation of PDGFRß.

Rationale: Long noncoding RNAs (lncRNAs) are emerging as important regulators of diverse biological functions. Their role in pulmonary arterial hypertension (PAH) remains to be explored.Objectives: To elucidate the role of TYKRIL (tyrosine kinase receptor-inducing lncRNA) as a regulator of p53/ PDGFRß (platelet-derived growth factor receptor ß) signaling pathway and to investigate its role in PAH.Methods: Pericytes and pulmonary arterial smooth muscle cells exposed to hypoxia and derived from patients with idiopathic PAH were analyzed with RNA sequencing. TYKRIL knockdown was performed in above-mentioned human primary cells and in precision-cut lung slices derived from patients with PAH.Measurements and Main Results: Using RNA sequencing data, TYKRIL was identified to be consistently upregulated in pericytes and pulmonary arterial smooth muscles cells exposed to hypoxia and derived from patients with idiopathic PAH. TYKRIL knockdown reversed the proproliferative (n = 3) and antiapoptotic (n = 3) phenotype induced under hypoxic and idiopathic PAH conditions. Owing to the poor species conservation of TYKRIL, ex vivo studies were performed in precision-cut lung slices from patients with PAH. Knockdown of TYKRIL in precision-cut lung slices decreased the vascular remodeling (n = 5). The number of proliferating cell nuclear antigen-positive cells in the vessels was decreased and the number of terminal deoxynucleotide transferase-mediated dUTP nick end label-positive cells in the vessels was increased in the LNA (locked nucleic acid)-treated group compared with control. Expression of PDGFRß, a key player in PAH, was found to strongly correlate with TYKRIL expression in the patient samples (n = 12), and TYKRIL knockdown decreased PDGFRß expression (n = 3). From the transcription factor-screening array, it was observed that TYKRIL knockdown increased the p53 activity, a known repressor of PDGFRß. RNA immunoprecipitation using various p53 mutants demonstrated that TYKRIL binds to the N-terminal of p53 (an important region for p300 interaction with p53). The proximity ligation assay revealed that TYKRIL interferes with the p53-p300 interaction (n = 3) and regulates p53 nuclear translocation.Conclusions: TYKRIL plays an important role in PAH by regulating the p53/PDGFRß axis.

[Successful treatment with imatinib for a patient with myeloid neoplasms with eosinophilia and abnormalities of PDGFRB due to t (5;14)(q33;q22)].

A 50-year old man with a 1-year history of eosinophilia presented with an eosinophil count exceeding 13,800/mm3 in the peripheral blood at the first visit. Bone marrow examination revealed that eosinophils accounted for 30% of the nucleated cell count, and G-band karyotyping analysis detected t (5;14)(q33;q22). Using peripheral blood FISH test, he was found to have platelet-derived growth factor receptor ß (PDGFRB) locus rearrangement at 5q32-33. The level of eosinophils in the peripheral blood reduced markedly 3 days after the initiation of Imatinib mesylate, 400 mg daily. This treatment was administered for 2 years, after which the peripheral blood FISH test was negative for PDGFRB. In this disease, although most cases are with t (5;12), those with t (5;14) are relatively rare, and the long-term course of this translocation is unknown.

Multiple routes of endocytic internalization of PDGFRß contribute to PDGF-induced STAT3 signaling.

Platelet-derived growth factor receptor ß (PDGFRß) is a receptor tyrosine kinase which upon activation by PDGF-BB stimulates cell proliferation, migration and angiogenesis. Ligand binding induces intracellular signaling cascades but also internalization of the receptor, eventually resulting in its lysosomal degradation. However, endocytic trafficking of receptors often modulates their downstream signaling. We previously reported that internalization of PDGFRß occurs via dynamin-dependent and -independent pathways but their further molecular determinants remained unknown. Here we show that, in human fibroblasts expressing endogenous PDGFRß and stimulated with 50 ng/ml PDGF-BB, ligand-receptor uptake proceeds via the parallel routes of clathrin-mediated endocytosis (CME) and clathrin-independent endocytosis (CIE). CME involves the canonical AP2 complex as a clathrin adaptor, while CIE requires RhoA-ROCK, Cdc42 and galectin-3, the latter indicating lectin-mediated internalization via clathrin-independent carriers (CLICs). Although different uptake routes appear to be partly interdependent, they cannot fully substitute for each other. Strikingly, inhibition of any internalization mechanism impaired activation of STAT3 but not of other downstream effectors of PDGFRß. Our data indicate that multiple routes of internalization of PDGFRß contribute to a transcriptional and mitogenic response of cells to PDGF.

The rise of soluble platelet-derived growth factor receptor ß in CSF early after subarachnoid hemorrhage correlates with cerebral vasospasm.

Platelet-derived growth factor ß (PDGFß) has been proposed to contribute to the development of cerebral vasospasm (CVS) after subarachnoid hemorrhage (SAH), and soluble PDGFRß (sPDGFRß) is considered to be an inhibitor of PDGF signaling. We aimed at determining the sPDGFRß concentrations in the cerebrospinal fluid (CSF) of patients with aneurysmal SAH (aSAH) and analyzing the relationship between sPDGFRß level and CVS. CSF was sampled from 32 patients who suffered aSAH and five normal controls. Enzyme-linked immunosorbent assay was performed to determine the sPDGFRß concentrations in the CSF. Functional outcome was assessed using modified Rankin scale (mRS) at 6 months after aSAH. CVS was identified using transcranial Doppler or angio-CT or DSA. The cutoff of sPDGFRß for CVS was defined on the ROC curve. The concentrations of sPDGFRß following aSAH were both higher than those of normal controls on days 1-3 and 4-6, and peaked on days 7-9 post-SAH. The cutoff value of sPDGFRß level on days 1-3 for CVS was defined as 975.38 pg/ml according to the ROC curve (AUC = 0.680, p = 0.082). In addition, CSF sPDGFRß concentrations correlated with CVS (r = 0.416, p = 0.018), and multivariate analysis indicated that sPDGFRß level higher than 975.38 pg/ml on days 1-3 was an independent predictor of CVS (p = 0.001, OR = 19.22, 95% CI: 3.27-113.03), but not for unfavorable outcome after aSAH in the current study. CSF sPDGFRß level increases after aSAH and is higher in patients who developed CVS, and sPDGFRß level higher than 975.38 pg/ml on days 1-3 is a potential predictor for CVS after SAH.

Ablation of Pericyte-Like Cells in Lungs by Oropharyngeal Aspiration of Diphtheria Toxin.

We demonstrated previously that FoxD1-derived cells in the lung are enriched in pericyte-like cells in mouse lung. These cells express the common pericyte markers and are located adjacent to endothelial cells. In this study, we demonstrate the feasibility of administering diphtheria toxin (DT) by oropharyngeal aspiration as an approach to ablating FoxD1-derived cells. We crossed mice expressing Cre-recombinase under the FoxD1 promoter to Rosa26-loxP-STOP-loxP-iDTR mice and generated a bitransgenic line (FoxD1-Cre;Rs26-iDTR) in which FoxD1-derived cells heritably express simian or human diphtheria toxin receptor and are sensitive to DT. We delivered low-dose (0.5 ng/g) and high-dose (1ng/g × 2) to FoxD1-Cre;Rs26-iDTR mice and littermate control mice by oropharyngeal aspiration and evaluated ablation by flow cytometry and immunohistochemistry. FoxD1-Cre mice showed a 40-50% reduction in PDGFRß+ cells by flow cytometry at Days 2 and 7 after DT administration, with a return of PDGFRß+ cells at Day 28. Confocal microscopy revealed an observable reduction in pericyte markers. Bronchoalveolar lavage fluid analysis revealed no significant differences in total protein, bronchoalveolar lavage fluid red blood cell, or white blood cell counts at low dose. However, at high-dose DT, there was a proinflammatory effect in the control mice and increased mortality associated with systemic toxicity in Cre+ mice. Low-dose DT reduced lung PDGFRß+ stromal cells in the FoxD1-Cre;iDTR transgenic model without a differential effect on lung inflammation in DT-sensitive and DT-insensitive animals. Low-dose DT is a viable method for transient lineage-specific stromal cell ablation in the lung that minimizes systemic toxicity.

Effects of high fat diet and perinatal dioxin exposure on development of body size and expression of platelet-derived growth factor receptor ß in the rat brain.

Environmental exposure to dioxins, consumption of a high fat diet, and platelet-derived growth factor receptor ß signaling in the brain affect feeding behavior, which is an important determinant of body growth. In the present study, we investigated the effects of prenatal exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin and high fact diet after weaning on body growth and expression of platelet-derived growth factor receptor ß in the brain in rat pups. Subjects from the control and dioxin exposure groups were assigned to 1 of 3 different diet groups: standard diet, high fat diet in the juvenile period, or high fat diet in adulthood. Body weight gain rate in the juvenile high fat diet group and the length gain rate in the adult high fat diet group were greater than the corresponding values in the standard diet group only in male offspring, although the effects of dioxin exposure on growth were not significant. Consumption of a high fat diet decreased platelet-derived growth factor receptor ß levels in the amygdala and hippocampus in both sexes compared to control groups, while 2,3,7,8-tetrachlorodibenzo-p-dioxin decreased platelet-derived growth factor receptor platelet-derived growth factor receptor ß levels in the amygdala and striatum only in females receiving an high fat diet. Furthermore, platelet-derived growth factor receptor ß levels in the hippocampus and platelet-derived growth factor receptor ß striatum were inversely correlated with increases in body length, while changes in platelet-derived growth factor receptor ß in the amygdala and nucleus accumbens were significantly correlated to body weight gain or body mass index. In conclusion, these findings suggest that these 2,3,7,8-tetrachlorodibenzo-p-dioxin and high fat diet-induced changes in body growth and feeding behaviors might be partially mediated by changes in brain platelet-derived growth factor receptor ß levels.

Tracking anti-fibrotic pathways of nilotinib and imatinib in experimentally induced liver fibrosis: an insight.

The tyrosine kinase inhibitors imatinib and nilotinib have been suggested to have promising antifibrotic activity in experimental models of liver fibrosis. The aim of the present study was to investigate new pathways underlying this beneficial effect. Hepatic injury was induced in male Wistar rats by intraperitoneal injection of CCl4 for 12 weeks. During the last 8 weeks of treatment, rats were also injected daily intraperitoneally with 20 mg/kg imatinib or 20, 10 or 5 mg/kg nilotinib. At the end of treatment, effects on fibrosis were assessed by measuring serum fibrotic markers and profibrogenic cytokines, as well as by histopathological examination. Possible anti-inflammatory effects were estimated by measuring levels of inflammatory cytokines in liver tissue. Liver expression of α-smooth muscle actin, transforming growth factor (TGF)-ß1 antibodies and platelet-derived growth factor receptor ß (PDGFRß) was evaluated by immunohistochemical staining techniques. Nilotinib (5 and 10 mg/kg) significantly (P < 0.05) decreased all serum fibrotic markers measured, but 20 mg/kg of either nilotinib or imatinib had limited effects. At all doses tested, nilotinib significantly (P < 0.05) decreased the CCl4 -induced increases in tissue inflammatory cytokines. Furthermore, 5 and 10 mg/kg nilotinib significantly decreased TGF-ß1 levels and tissue expression of its antibody, as well expression of PDGFRß. In conclusion, low doses (5 and 10 but not 20 mg/kg) of nilotinib, rather than imatinib, can control hepatic fibrosis by regulating levels of proinflammatory cytokines, primarily interleukin (IL)-1 and IL-6. Nilotinib also controls the signalling pathways of profibrogenic cytokines by lowering TGF-ß1 levels and decreasing expression of PDGFRß.

Platelet-derived Growth Factor Activates Pericytes in the Microvessels of Chronic Subdural Hematoma Outer Membranes.

Angiogenesis is one of the growth mechanisms of chronic subdural hematoma (CSDH). Pericytes have been implicated in the capillary sprouting during angiogenesis and are involved in brain ischemia and diabetic retinopathy. This study examined the pericyte expressions in CSDH outer membranes obtained during trepanation surgery. Eight samples of CSDH outer membranes and 35 samples of CSDH fluid were included. NG2, N-cadherin, VE-cadherin, Tie-2, endothelial nitric oxide synthase (eNOS), platelet-derived growth factor (PDGF) receptor-ß (PDGFR-ß), a well-known marker of pericytes, phosphorylated PDGFR-ß at Tyr751, and ß-actin expressions, were examined using western blot analysis. PDGFR-ß, N-cadherin, and Tie-2 expression levels were also examined using immunohistochemistry. The concentrations of PDGF-BB in CSDH fluid samples were measured using enzyme-linked immunosorbent assay kits. NG2, N-cadherin, VE-cadherin, Tie-2, eNOS, PDGFR-ß, and eNOS expressions in CSDH outer membranes were confirmed in all cases. Furthermore, phosphorylated PDGFR-ß at Tyr751 was also detected. In addition, PDGFR-ß, N-cadherin, and Tie-2 expressions were localized to the endothelial cells of the vessels within CSDH outer membranes by immunohistochemistry. The concentration of PDGF-BB in CSDH fluids was significantly higher than that in cerebrospinal fluid. These findings indicate that PDGF activates pericytes in the microvessels of CSDH outer membranes and suggest that pericytes are crucial in CSDH angiogenesis through the PDGF/PDGFR-ß signaling pathway.